The instant invention relates to welding apparatus and more particularly to a resistance welding apparatus which is adapted to minimize arcing during a welding operation.
The concept of resistance welding is extremely well known and has been utilized in a wide variety of applications. In this regard, resistance welding is based on the principal of passing a relatively high electrical current through a metal component in order to heat the metal in the current path therethrough to a temperature above the melting point of the metal in the component. More specifically, a resistance welding operation is carried out by contacting a metal workpiece assembly comprising a pair of workpieces, or a pair of workpieces and a welding material, with a pair of electrodes in order to pass a relatively high electrical current through the workpiece assembly. When an electrical current is passed through a workpiece assembly in this manner the resistances of the electrodes and of the metal components in the workpiece assembly cause the metal in the current path through at least one of the metal components to be heated to a temperature above the melting point thereof in order to weld the melted component to one or more adjacent components in the workpiece assembly.
It has been found that the main variables in a resistance welding operation of the above described type are current, welding time, and electrode force. In this regard, it has been found that by altering the amount of current delivered to a workpiece assembly, or the welding time during which current is delivered thereto, it is possible to vary the amount of power delivered to the workpiece assembly in order to vary the amount of heat generated at the welding site. However, it has also been found that if the electrodes utilized in a welding operation are not applied to a workpiece assembly with sufficient levels of contact force, relatively high contact resistances can develop between the electrodes and the workpiece assembly causing arcing to occur in of the areas where one or both of the electrodes contact the workpiece assembly. It has been further found that arcing can cause blow holes and/or distortion in the metal components of a workpiece assembly and that as a result it can be extremely important to control the contact forces applied to a workpiece assembly by a pair of electrodes during a welding operation. Although it can be a relatively simple matter to maintain the proper levels of contact force when performing a welding operation utilizing an automated welding apparatus which is operative for mechanically aligning and contacting the electrodes thereof with a workpiece assembly it can be much more difficult to manually align and apply the electrodes of a manually operable welding apparatus to a workpiece assembly with sufficient levels of contact force to avoid arcing. As a result, it has been found that arcing can often occur when welding a operation is carried out utilizing conventional welding apparatus comprising one or more hand held electrodes. Further, since manually operable welding apparatus comprising one or more hand held electrodes have frequently been utilized for performing various precision welding operations in the manufacture of certain electrical components as well as in the manufacture of various jewelry items, arcing has represented a significant manufacturing problem in both the electronics industry and the jewelry industry.
The instant invention provides an effective solution to the problem of arcing during resistance welding. Specifically, the instant invention provides a welding apparatus which is operative for sensing the contact resistances between a pair of electrodes and a workpiece assembly, and for controlling the application of power to the workpiece assembly so that a welding operation can only be carried out when the contact resistances are below a predetermined threshold level. Hence, the apparatus of the instant invention is adapted so that a welding operation can only be carried out when the contact resistances between the electrodes thereof and a workpiece assembly are at levels which are unlikely to cause arcing. Still more specifically, the welding apparatus of the instant invention comprises first and second electrodes which are engageable with a workpiece assembly, power means which is operable for supplying a sufficient level of voltage potential across the electrodes and for passing a sufficient electrical current between the electrodes to carry out a welding operation, and resistance sensing means for sensing the resistance in the electrical circuit path between the electrodes. The welding apparatus further comprises the control means for comparing the sensed resistance in the electrical circuit path between electrodes with a predetermined threshold resistance value and for reducing the amount of power supplied to the electrodes through the power means in the event that the sensed resistance is above the threshold resistance value. The control means is preferably operable for reducing the amount of power supplied to the first and second electrodes by reducing the amount of current supplied to the electrodes, and the first electrode preferably comprises an electrode plate which is adapted for receiving a workpiece assembly thereon, whereas the second electrode preferably comprises a manually manipulatable electrode probe which is positionable in engagement with a workpiece assembly at a specific location thereon for performing a welding operation on the workpiece assembly. The apparatus preferably further includes current sensing means for sensing the magnitude of the current passing between the first and second electrodes and current control means for controlling the power means to maintain the magnitude of the current passing between the first and second electrodes at a predetermined level. The power means is preferably operable for passing a predetermined pattern of current pulses between the first and second electrodes and the current control means is preferably operative for maintaining the magnitude of the current pulses at a predetermined control level. Further, the probe is preferably constructed of a material having a sufficiently high resistance to cause the portion of the probe contacting a workpiece assembly during the welding operation to be heated to a temperature above the melting point of the material in the workpiece assembly contacted by the probe.
It has been found that the apparatus of the instant invention can be effectively utilized for carrying out a precision welding operation without arcing. In this regard, it has been found that because the apparatus of the instant invention is operative for sensing the contact resistances between the electrodes and a workpiece assembly and for energizing the electrodes to carry out a welding operation only in the event that the contact resistances are below a predetermined arcing threshold value, the apparatus can be effectively utilized for carrying out welding operations without arcing. In addition, because the apparatus of the instant invention is operative for precisely controlling the magnitude of the current passing between the electrodes thereof during a welding operation, the apparatus can be more effectively utilized for precisely and accurately applying the correct amount of power to a workpiece assembly to effect a welding operation thereon. Still further, because the apparatus of the instant invention preferably includes a relatively high resistance probe which is adapted so that it is heated to a temperature above the melting point of the metal in a workpiece assembly during a welding operation the probe of the apparatus of the instant invention is adapted to enhance a welding operation by increasing the amount of heat supplied to a workpiece assembly.
Accordingly, it is a primary object of the instant invention to provide a welding apparatus which is operable for carrying out a resistance welding operation without arcing.
Another object of the instant invention is to provide an effective resistance welding apparatus comprising a manually manipulatable electrode probe which is operative for carrying out a welding operation without arcing.
An even further object of the instant invention is to provide an effective welding apparatus for carrying out a resistance welding operation by passing a precisely controlled current level between a pair of welding electrodes.
An even still further object of the instant invention is to provide an apparatus for carrying out a resistance welding operation utilizing a high resistance electrode.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.